HIPS-GLAD core shell nanorod array photodetectors with enhanced photocurrent and reduced dark current. (13th October 2016) - Keles, Filiz
Abstract: Vertically aligned core/shell nanorod array photodetectors were fabricated by high pressure sputter (HIPS) deposition of copper indium sulfide (CIS) films on glancing angle deposited (GLAD) indium sulfide (In2 S3 ) nanorods. For comparison, we also studied nanorod photodetectors with conventional low pressure sputtered (LPS) CIS film coatings and counterpart thin film devices incorporating HIPS or LPS-CIS on In2 S3 films. HIPS-GLAD core/shell photodetectors have shown a superior photocurrent density response along with lowest dark current density. Photoresponsivity defined with the photocurrent density/dark current density ratio γ = | J ph / J dark | was about ∼1820 for HIPS-GLAD nanorod devices, which is several orders of magnitude higher compared to those of LPS-CIS thin film ( γ ∼ 2) and HIPS-CIS thin film ( γ ∼ 9) devices, and also about four-fold higher than LPS-CIS nanorod devices ( γ ∼ 490). Enhanced photoresponsivity is attributed to the porous microstructure and improved conformality of HIPS-CIS film around the In2 S3 nanorods confirmed by SEM and EDS measurements. Due to randomization of the sputtered flux at higher working gas pressures, HIPS can provide a more conformal while at the same time a voidy low-density film around nanostructured surfaces. Reduced interelectrode distance and improved p–n junction interface due to the more uniform conformality of HIPS-CIS result in a higher photocurrent in our HIPS-GLAD devices. In addition, the voids in HIPS-CIS film as a result of its porous nature can behave as highly resistive spots that lower the dark current. Therefore, we have demonstrated that by utilizing a simple and low-temperature HIPS-GLAD method, high-photocurrent and low-dark-current photodetectors can be achieved by controlling the conformality and microstructure of a shell layer around nanorod arrays. HIPS shell coating method can be extended to almost any type of nanostructured substrate.